The present invention relates to an apparatus and process for measuring the uncoiled length or coiled lenth of a cable of a winding gear such as a winch.
A problem arises in various fields of knowing exactly the coiled or uncoiled length of a cable with a view to determining with precision the position of its free end to which can be coupled a movable element, for example, a crane hook, a lift cage or a telpher railway cage, or further to measure the depth of a well or that of the extension of a string of rods or a fitment into a bore-hole.
Likewise, sooner than weighing, it is of interest to measure the coiled length of a cable or the like on a spool.
In another aspect, on a construction side, for example, it is of interest to a crane driver, with the jib overhanging an excavation the bottom of which he cannot see, but the depth of which can be indicated to him, so as to know the level at which the load he is manipulating is at.
In another connection, for cages or buckets of telpher railways, it is of interest at the command post to know exactly the position of a cage or bucket; this may be necessary in rescue cases for shifting an auxiliary relief chair or, in transporting concrete by providing a flow thereof to bridge piers or dams, for positioning of the charge so to avoid trial and error which can often be dangerous to personnel.
Finally, in the petroleum industry they use what are called "measuring captors" which serve to measure the advancement of a rod or a string of rods, devices which capitalize on the rotation of the winch main shaft, each turn on the winding drum of the winch being in fact counted as a mean circumference of the winding drum of the winch (mean length of a turn of cable).
Existing means for measuring the wound/unwound length of a cable is imprecise, because the length of each turn of cable which is wound tangentially in two subjacent turns is not the same in one layer of turns as another, the length of a turn in fact varies each time that a complete layer is rolled on or unrolled from the winding drum.
The present invention has for object to palliate the inconveniences of known means and it has for essential object a process and a means permitting, by algebraic summation of the real lengths of successive turns reeled off or reeled on by a winding gear to indicate exactly the length of cable unrolled from or rolled up on the winding drum of the winding gear, that is to say, in fact to specify the position of a load fixed to the free end of the cable.